Vice President Al Gore is not banging away on it. Perhaps that's because some trade unionists and other voters in such key swing states as Minnesota and Michigan are keen on their hunting weapons. Though Mr. Gore promises not to touch their rifles and shotguns, his call for background checks on private sales at gun shows may make these voters nervous.

Nor does Texas Gov. George W. Bush trumpet his opposing views, given the sensitivity of many women to gun violence. He already has the support of the National Rifle Association.

In any case, the campaign silence has not ended a shot-filled battle in the academic world.

Two years ago, John Lott Jr., then at the University of Chicago, came out with a book entitled, "More Guns, Less Crime" (University of Chicago Press). It held that waiting periods before gun buyers could take possession, gun buybacks, and background checks yield virtually no benefits in crime reduction. But "right to carry" laws, including legally concealed handguns, the book maintained, are the most cost-effective method for reducing violent crime, because criminals fear their victims may possess guns.

As one might expect, the Lott study became gospel for the gun lobby and gun enthusiasts.

But last week, the National Bureau of Economic Research published a paper by Mark Duggan, also from the University of Chicago, entitled "More Guns, More Crime." Increases in gun ownership, the study finds, lead to a higher gun-homicide rate, and concealed weapons do nothing to shrink crime.

At Harvard University's Kennedy School of Government, another economist, Philip Cook, talks of the Duggan paper "restoring common sense" to the gun discussion. It's hard to imagine, he adds, that "an armed citizenry" could accomplish the many good things outlined in the Lott book.

Contrariwise, gun violence costs the public far more than previously reckoned, according to a new book he has co-authored, "Gun Violence: The Real Costs" (Oxford University Press).

The costs are not just those resulting from gunshot injuries and deaths in terms of medical costs and lost productivity. Costs also arise from the fact that citizens move from violence-ridden inner cities to the suburbs. They pay more taxes to pay for the protection of public officials.

Homicides with guns, an effective weapon, cost the justice system more than the criminal-assault cases that usually arise from less-deadly weapons. Costly security measures at airports, schools, and other public buildings try to detect guns.

Altogether, there are an estimated 200 million plus guns in the United States. They are involved in 70 percent of homicides and a substantial share of other violent crimes.

From 1993 to 1998, gun homicides dropped 36 percent while nongun homicides declined only 18 percent. In that same period, the fraction of households with at least one gun fell from more than 42 percent to 35 percent.

About one-third of the gun-homicide decline is explained by the fall in gun ownership, Mr. Duggan reckons. The largest declines occur in areas with the largest reductions in firearms ownership.

To reach this conclusion, Duggan devised a unique method for determining levels and changes in gun ownership at the state and county level. He used subscription data for one of the nation's largest gun magazines, Guns &amp; Ammo. This got around the geographical imprecision that has plagued previous studies of the impact of guns on crime. Duggan's magazine data squared with county gun sales and the death rate from gun accidents, gun-show data, and NRA membership data.

Mr. Lott, now at Yale University Law School, says gun-ownership levels may merely reflect shifts in crime levels. More crime results in more guns for protection.

Duggan refutes this by noting that nongun homicides do not fall when gun ownership declines, though gun homicides do drop.

Steven Levitt, an economist specializing in gun issues, also at the University of Chicago, calls Duggan's report "extremely insightful." The paper has been accepted for publication by the prestigious Journal of Political Economy.